As the resolution of mobile devices increases, source amplifiers in the source driver may need to drive display panels faster. In addition to increased speed, however, it is also desirable to maintain relatively low power consumption to conserve battery life in devices, such as mobile phones, personal digital assistants, and the like. For example, the bias current of a typical mobile Liquid Crystal Display Integrated Circuit (LDI) source driver amplifier is less than 1 μA. However, there may be hundreds of source driver amplifiers in an LDI so even relatively small increases in the bias current of a source driver amplifier may significantly shorten battery life.
FIG. 1 illustrates a conventional source driver amplifier circuit that is configured as a unity-gain buffer in which the output node VOUT is connected to the negative input node inn. FIGS. 2A and 2B illustrate plots of an input voltage waveform applied to the amplifier of FIG. 1 and the output voltage waveform generated in response to the input voltage waveform, respectively. The input voltage waveform changes at the beginning of a new row-line scan as shown in FIG. 2A. The source driver amplifier drives the column line of the display panel in response to the input voltage waveform. As shown in FIG. 2B, the driving time for generating the output voltage waveform is influenced primarily by the slew rate of the source driver amplifier. The slew rate (SR) may be expressed as follows: SR=Ib/Cm, where Ib is the tail current of the input differential stage and Cm is the capacitance of the compensation capacitors. The source driver amplifier circuit of FIG. 1 includes two compensation capacitors CP and CN. Because the bias current of a conventional source driver amplifier is relatively small, the dominant factor that limits the driving time of the amplifier is the speed at which the compensation capacitors can be charged and discharged.
Also, in Korean patent application No. 10-2004-0077156, a technology (hereinafter, “FSR technology”) that is capable of improving slew rate by changing total capacitance of compensation capacitors according to each operational section of an amplifier, is provided. According to FSR technology, the time period allocated to performing the slewing is changed according to a level of an input voltage at the beginning of the operation. Therefore, the settling time of each operational time period can be different according to the difference between a current voltage level and an input voltage level of the next operational section.